Polymerization of Phenylacetylenes with Rhodium Zwitterionic Complexes: Enhanced Catalytic Activity by π-Acidic Diene Ligands

Zwitterionic Rh catalysts bearing a series of tetrafluorobenzobarrelene (tfb) ligands proved to be highly active in the polymerization of phenylacetylenes. The highest catalytic activity for the polymerization of phenylacetylene was observed with (tfb)Rh<sup>+</sup>[(η<sup>6</sup>-Ph)B<sup>−</sup>Ph<sub>3</sub>] (<b>1</b>). Catalyst <b>1</b> displayed higher activity to produce higher molecular weight polymer than the conventional nbd analogue, (nbd)Rh<sup>+</sup>[(η<sup>6</sup>-Ph)B<sup>−</sup>Ph<sub>3</sub>] (<b>5</b>, nbd = 2,5-norbornadiene). In the case of other zwitterionic Rh catalysts bearing polymethylated tfb ligands [tfb-Me<sub>2</sub>, <b>2</b>; tfb-Me<sub>3</sub>, <b>3</b>; tfb-Me<sub>4</sub>, <b>4</b>], the catalytic activity tended to decrease with increasing number of the incorporated methyl groups. Catalyst <b>1</b> also showed high activity in the polymerization of phenylacetylene derivatives irrespective of electron-donating or -withdrawing nature of ring-substituents of the monomers.